The present invention relates to method of forming a thin film on a surface of a substrate by physical vapor deposition.
In the prior art, ion plating method or cluster ion beam method is also known as physical vapor deposition and the thin film which is formed by this method. In such method, a material which is to form a thin film is evaporated, and particles of the vapor are ionized; the ionized vapor particles are accelerated by applying high voltage between the evaporation source and the substrate. The particles supplied with large kinetic energy collide with the substrate, thereby forming a strongly adhering film on the substrate.
It is known that the thin film formed by the ionized vapor particles has excellent crystal properties in comparison with the thin film obtained without ionizing the vapor particles. This is because the former has the large kinetic energy supplied to the ions.
However, the thin film formed in such method is apt to be deposited in a polycrystalline state rather than a monocrystalline state.
That is, as shown in FIG. 2, an ionized vapor particle 1 of thin film material flies towards a substrate 4 along dotted line by means of attraction of charges induced on growth steps 2, 3 of a thin film being formed on a surface of the substrate 4. When the vapor particle 1 is sufficiently close to the substrate 4, the vapor particle 1 is subjected to the attraction of the nearer growth step 2 and varies the orbit of the dotted line and is directed towards the growth step 2. However, since application of the high voltage is maintenance, the vapor particle 1 is accelerated into high speed and therefore cannot attain the growth step 2 but collides with certain position 5 of the substrate 4. Subsequently, it is preferable that the vapor particle 1 can be moved to the growth step 2 according to the kinetic energy supplied to the vapor particle 1. If the vapor particle 1 cannot be moved to the growth step 2, it stops at the position 5 on the surface of the substrate 4 with which the vapor particle 1 collides or at any position between the position 5 and the growth step 2. New growth of the thin film starts from the stop position of the vapor particle 1. Thus the formed thin film becomes polycrystalline, i.e. a collection of many fine crystals but does not become a thin film of single crystal.
The vapor particle 1 of the thin film material in this case an atom or molecule of the thin film material or a fine atomic group as a collection of several atoms in the ion plating, or a massive atomic group (cluster) where atoms of several thousands or less in number of the thin film material are loosely coupled in the cluster ion beam method.
As above described, the thin film of single crystal or that close to single crystal cannot be formed by a conventional method. Particularly, in the semiconductor technology, the thin film of single crystal of semiconductor must be formed on the substrate. However, since the thin polycrystalline film of is formed in the conventional method, this method cannot be used to produce semiconductor device.